Python Array Item Remove

Question

I have some Python experience, but (obviously) not an overwhelming wealth of knowledge. In short, I need to create validation arrays for Neural Network testing using 1/5th of a main array. So, I am able to append i % 5 == 0 values to a test array. From there, I can still print every 5th value. Now, when I go to remove values, I get the out of index or range error; I know it is because the remove is changing the overall value of len(string_arr). However, I have been unsuccessful in figuring out a way to compensate.

Below is a 'dummy' program to solve what I need, but not the actual thing I am working on. I need 1/5th on a validation array, remove that 1/5th from the main array, and have 4/5th left on the main to train on. Below, I tried to appended to another array and remove those values in order to not mess up the len(string_arr)... did not work.

Thank you

english_list = open('file')
for word in english_list.readlines():
word = word[:-1].lower()
if len(word) == 6:
    string_arr.append(word)
    target_arr.append(0)
print(string_arr)
print(len(string_arr))


for i in range(len(string_arr)):
    if i % 5 == 0:
        test_arr.append(string_arr[i])

for i in range(len(string_arr)):
    if i % 5 == 0:
        one_more.append(string_arr[i])

for i in range(len(string_arr)):
    if one_more[i] == string_arr:
        string_arr.remove(one_more[i])

print(test_arr)
print(len(test_arr))
print(string_arr)
print(len(string_arr))

Can you use external libraries? If so check this method from sklearn — josepdecid
– josepdecid, Commented Feb 27, 2019 at 14:07
Perhaps you would like to correct the indentation of your code so it is runnable and makes sense. — khelwood
– khelwood, Commented Feb 27, 2019 at 14:08
@JosepJoestar thank you and I am aware of some of the simplicity the sklearn adds to all this, but I must create the separate arrays — Sam Dean
– Sam Dean, Commented Feb 27, 2019 at 14:33

Taylor Nelms · Accepted Answer · 2019-02-27 14:28:12Z

1

You can do it in a slightly more compact manner with fancy list indexing:

small_cut = string_arr[::5]
remaining = [j for sub in zip(string_arr[1::5], string_arr[2::5], string_arr[3::5], string_arr[4::5]) for j in sub]

This is assuming you're working with normal python lists; if you're working with something like a numPy array, there might be even easier approaches (potentially more efficient, too) to do what you want.

answered Feb 27, 2019 at 14:28

Taylor Nelms

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3 Comments

bruno desthuilliers Over a year ago

NameError: name 'j' is not defined

Taylor Nelms Over a year ago

@brunodesthuilliers did you get the whole line?

bruno desthuilliers Over a year ago

err... copy-paste issue indeed, my bad xD

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